The present invention relates to a separator for an electrochemical device, a manufacturing method thereof, and an electrochemical device comprising the same.
Recently, there is an increasing interest in energy storage technologies. As the application fields of energy storage technologies have been extended to mobile phones, camcorders, notebook computers, and even electric cars, efforts towards the research and development on electrochemical devices have been increasing. In aspect of the above situation, rechargeable secondary batteries are at the center of attention as the most favorable electrochemical device. Lately, many studies have been done to design new electrodes and batteries to improve the capacity density and specific energy of the batteries.
Among currently available secondary batteries, lithium secondary batteries developed in the early 1990's have drawn attention for their higher operating voltage and much higher energy density than those of conventional batteries using an aqueous electrolyte such as Ni-MH batteries, Ni—Cd batteries, and H2SO4—Pb batteries. However, lithium secondary batteries have shortcomings such as a complicate manufacturing process and safety-related problems caused by the use of an organic electrolyte, for example, firing, explosion, and the like. Lithium-ion polymer batteries that have settled the drawbacks of lithium ion batteries are considered as one of the next-generation batteries. However, lithium-ion polymer batteries have a relatively lower battery capacity than lithium ion batteries, and in particular, have an insufficient discharging capacity at low temperature. Accordingly, there is an urgent need to solve these disadvantages of lithium-ion polymer batteries.
A variety of electrochemical devices are being produced from many different companies, and they all exhibit different safety characteristics. Thus, it is important to evaluate and ensure the safety of electrochemical devices. The most important factor to consider is that electrochemical devices should not cause any damage to users due to malfunction. Taking this into account, Safety Regulations strictly prohibit safety-related accidents of electrochemical devices such as firing or smoke emission. According to the safety characteristics of electrochemical devices, thermal runaway caused by overheating of an electrochemical device or puncture of a separator may increase the risk of explosion.
In particular, a polyolefin-based porous membrane conventionally used as a separator for an electrochemical device may show severe thermal shrinkage behaviors when the electrochemical device is subject to thermal runaway, thereby resulting in a short circuit between a cathode and an anode. Meanwhile, a conventional separator such as a polyolefin-based porous membrane has poor wettability to an electrolyte, which may have a negative influence on improving the performance of an electrochemical device.
Accordingly, there is a need for a separator with excellent heat resistance and wettability to an electrolyte.
Therefore, it is an object of the invention to provide a separator having improved heat resistance and wettability to an electrolyte that can replace a conventional separator, a manufacturing method thereof, and an electrochemical device comprising the same.